The wheel bearing apparatus for supporting a vehicle wheel that freely rotatably supports a wheel hub for mounting a wheel, via a rolling bearing, is used for driving wheels and driven wheels. For structural reasons, the inner ring rotation type is used for driving wheels and both the inner ring rotation type and the outer ring rotation type are used for driven wheels. In such a wheel bearing apparatus, a double row angular contact ball bearing is widely used. The double row angular contact bearing has several merits, such as a desirable bearing rigidity, a high durability against misalignment, and a small rotational torque resistance contributing to improved fuel consumption. On the other hand a double row angular contact tapered roller bearing is used for heavy weight vehicles such as off-road cars and trucks, etc.
These types of wheel bearing apparatus are arranged at places liable to be splashed by muddy water. Thus, they are provided with a sealing apparatus to seal spaces between outer and inner members. In general, a sealing member with sealing lips, of the sealing apparatus, is mounted on the outer member to form a secured member. The sealing lips are adapted to be in sliding contact with an outer circumferential surface of the inner member. Several mechanisms to improve sealability have been used, especially in vehicles used in severe circumstances such as off-road cars and trucks, etc.
One example of such wheel bearing apparatus is shown in FIG. 23. The wheel bearing apparatus includes a knuckle 51 secured on a chassis. An axle 52 extends through the knuckle 51. A wheel hub 54 is mounted on the axle 52. A wheel (not shown) is fastened via bolts 53 to the wheel hub 54. A wheel bearing 55 rotationally supports the wheel hub 54 and the axle 52. A clutch 56, controlled by pneumatic pressure, engages and disengages the axle 52 and the wheel hub 54.
An annular chamber (vacuum chamber) 57 is formed between the knuckle 51 and the axle 52 and communicates with the clutch 56 arranged within a sealed chamber 58, of the outer side (right-hand side in FIG. 23). A negative pressure acts on the clutch 56 and the clutch 56 acts to engage the axle 52 and the wheel hub 54 when the pressure within the annular chamber 57 is lower than atmospheric pressure. The clutch 56 acts to disengage them when the annular chamber 57 is at atmospheric pressure. The annular chamber 57 communicates with a vacuum pump (not shown) via a vacuum passage 59 that obliquely extends through the knuckle 51.
The wheel bearing 55 is a double row tapered roller bearing with an outer member 60 formed on its outer circumference with a body mounting flange 60b that is mounted on the knuckle 51. Its inner circumference has double row tapered outer raceway surfaces 60a, 60a. Inner rings 61, 62 are formed on their outer circumference, with tapered inner raceway surfaces 61a, 62a that oppose the double row outer raceway surfaces 60a, 60a, respectively. Double row tapered rollers 63, 63 are contained between the outer and inner raceway surfaces 60a, 60a: 61a, 62a. Cages 64, 64 freely rollably hold the double row tapered rollers 63, 63.
The wheel hub 54 has a wheel mounting flange 65 integrally formed at one end. A cylindrical portion 54a axially extends from the wheel mounting flange 65. The wheel bearing 55 is press fit onto the cylindrical portion 54a of the wheel hub 54. It is axially immovably secured by a securing nut 66. A sliding bearing 67 is arranged between the axle 52 and the wheel hub 54 to allow a relative rotation between the two.
Seals 68, 69 are arranged at both ends of the wheel bearing 55. They seal openings of the annular spaces formed between the outer member 60 and the inner rings 61, 62. Also, the seals isolate the annular chamber 57 from the surrounding circumstances. The seal 68 includes an outer case 70 press fit into the outer member 60 and an inner case 71 press fit onto the inner rings 61. Sealing lips 70a, 71a are integrally bonded to an inner circumference of the outer case 70 and an outer circumference of the inner case 71 so that they slidingly contact the case 71 and the outer case 70, respectively. These sealing lips 70a, 71a can be deflected by a pressure difference between the inside of the wheel bearing 55 and the annular chamber 57. This discharges air within the inside of the wheel bearing 55 to the annular chamber 57. Accordingly, the pressure of the inside of the wheel bearing 55 becomes the same pressure as that in the annular chamber 57 when the annular chamber 57 is evacuated.
The seal 69 includes an outer case 72 press fit into the outer member 60. An inner case 73 is press fit onto the inner ring 62, as shown in FIG. 24. A sealing lip 72a slidingly contacts the inner case 73. A side lip 72b slidingly contacts a side face of the wheel mounting flange 65. Both are integrally bonded to both ends of the outer case 72. In addition, a sealing lip 73a is integrally bonded to an outer circumferential edge of the inner case 73. This seal 69 functions to apply a pressure difference so that the inside of the wheel bearing 55 can be held at a predetermined reduced pressure. This prevents rain water or dusts from entering into the inside of the wheel bearing. Japanese Laid-open Patent Application No. 2001/510534
In the prior wheel bearing apparatus, it is possible to have excellent sealing properties since a side lip 72b is provided in sliding contact with the side face of the wheel mounting flange 65. In addition, sealing lips 72a, 73a are in sliding contact with the inner and outer cases 72, 73, respectively. However, since it is configured so that the side lip 72b is in direct sliding contact with the side face of the wheel mounting flange 65, the side face of the wheel mounting flange 65, with which the side lip 72b contacts, should be finished to have a predetermined surface roughness. This increases the machining steps and thus the manufacturing cost. Furthermore, corrosion would be easily generated on the surface of the wheel hub 54 made of carbon steel. Accordingly, it is difficult to keep a stable seal for a long term in the structure where the side lip 72b directly contacts the side face of the wheel mounting flange 65. The side lip 72b is prematurely deteriorated by the corroded side surface of the wheel mounting flange 65.